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# What is meant by quantifier? Name the various quantifier used in c++

In C++, quantifiers are special symbols that are used in regular expressions to specify the number of times a character, group of characters, or pattern should occur. There are several quantifiers available in C++, including the following:

1. `*`: The `*` quantifier specifies that the preceding character, group of characters, or pattern should occur zero or more times. For example, `a*` matches zero or more `a` characters.
2. `+`: The `+` quantifier specifies that the preceding character, group of characters, or pattern should occur one or more times. For example, `a+` matches one or more `a` characters.
3. `?`: The `?` quantifier specifies that the preceding character, group of characters, or pattern should occur zero or one time. For example, `a?` matches zero or one `a` characters.
4. `{n}`: The `{n}` quantifier specifies that the preceding character, group of characters, or pattern should occur exactly `n` times. For example, `a{3}` matches exactly three `a` characters.
5. `{n,}`: The `{n,}` quantifier specifies that the preceding character, group of characters, or pattern should occur at least `n` times. For example, `a{3,}` matches at least three `a` characters.
6. `{n,m}`: The `{n,m}` quantifier specifies that the preceding character, group of characters, or pattern should occur at least `n` times, but no more than `m` times. For example, `a{3,5}` matches at least three `a` characters, but no more than five `a` characters.

Here is an example of how to use quantifiers in a regular expression in C++:

``````#include <iostream>
#include <regex>

int main()
{
std::string s = "aaaabbbbccccdddd";
std::regex r("a*b+c{2,4}d{2}");
if (std::regex_match(s, r))
{
std::cout << "Match found!" << std::endl;
}
else
{
In this example, the regular expression `a*b+c{2,4}d{2}` uses all of the quantifiers listed above. It matches a string that contains zero or more `a` characters, one or more `b` characters, two to four `c` characters, and exactly two `d` characters. In this case, the string `"aaaabbbbccccdddd"` matches the regular expression, so the output is “Match found!”.